Hierarchical Storage Management (HSM) is a technique that allows storing data on the most appropriate storage medium over the lifecycle of the data. HSM is implemented on a storage system that includes at least two tiers of storage, for example one tier provided by hard disk drives and one tier provided by tapes. Data is first placed on the first tier of storage (such as disk) and later migrated to the second tier (such as tape). Thereby the access to the data migrated to the second tier is transparent via the first tier. HSM may be implemented on file systems whereby the data subject for migration is a file or directory. HSM may also be implemented on block storage systems whereby the data subject for migration is a block. Thus data can be a file, an object or a block.